Methods for synthesizing an optically active form of a chiral compound are roughly classified into the following three methods: (1) method in which an optically active compound is employed as a starting raw material; (2) method in which a racemic mixture is optically resolved; and (3) asymmetric synthesis method using an asymmetric catalyst.
In the method (2), a target compound is resolved as a diastereomer from a racemic mixture after formation of a salt by use of an optically active carboxylic acid or amine, or after esterification or amidation by use of an optically active carboxylic acid. Amines or carboxylic acids derived from natural products may be employed as a resolution reagent, but employment of such a reagent results in a low optical resolution yield of a racemic mixture. Therefore, in order to obtain a wider range of target compounds, a novel resolution agent must be provided.
In the method (3), a large quantity of optically active compounds can be synthesized by use of a catalytic amount of another optically active compound, and thus the method is most economical and effective. Enzymes derived from organisms or chemically synthesized catalysts may be employed as a catalyst for asymmetric synthesis. Of these, enzymes derived from organisms are chemically unstable and have disadvantageously high substrate specificity, and thus such enzymes are not generally employed. Meanwhile, few asymmetric catalysts are available that are easily synthesized and have high asymmetric yield and chemical yield, although a variety of chemically synthesized asymmetrical catalysts are available.
In view of the foregoing, an object of the present invention is to provide a compound which is easily synthesized and serves as an optical resolution agent that can attain a high optical resolution percentage, and a compound which is easily synthesized and serves as an asymmetric synthesis catalyst that can attain high asymmetric yield and chemical yield.